Since the discovery of the high temperature superconductivity of YBa.sub.2 Cu.sub.3 O.sub.7-x material at about 95 K, worldwide efforts have centered on wire fabrication for applications in the areas of power generation, power transmission lines and passive microwave components such as helical resonators used in the telecommunication industry. However, these and related oxide superconductors are usually brittle and difficult to fabricate into useful shapes such as tapes, wires, or coils. Additionally, advanced processing techniques, e.g. melt texturing or zone melting, are required to texture the grains, i.e. align the grains along the anisotropic a-b conducting plane, to enhance critical current densities in the fabricated wires, etc.
As a consequence of the anisotropic nature of the superconductivity of such materials, their critical temperature, critical current density, and microwave properties have been found to be greatly influenced by their microstructures which, in turn, are largely determined by the fabrication process used. Practical wire applications for power generation will necessitate a critical density of the order of 100,000 A/cm.sup.2 in magnetic fields up to 5 Tesla, whereas homogeneity of the bulk material and surface smoothness are critical to the material's application in microwave circuits. Therefore, novel materials processing methods are required to reduce defects, to enhance mechanical and electrical properties of the superconducting materials, and to enhance reproducibility.
In particular, the anisotropy and grain boundary effects have been identified as major contributors to low critical current density in, e.g., yttrium barium copper oxide superconducting materials. The granular structure results in small coherence length, causing the grain boundaries to act as Josephson junctions. The high degree of anisotropy suppresses tunneling currents at high-angle grain boundaries. These problems are exacerbated by residual porosity in the densified material.
Several processing techniques have been studied in attempts to improve these properties, including those based on cladding/swaging techniques borrowed from the metallurgical industry and others based on the fiber spinning and extrusion techniques used in the plastics industry. The cladding/swaging methods have shown promise, in some cases producing wires with high ductility and workability. However, the spinning and extrusion techniques have generally produced only brittle, inhomogeneous materials.